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Jan van Helmont (1600s)He weighed a pot of soil before and after he planted a willow tree in it | He only gave it water for five years | The pot weighed the same afterwards but the tree was seventy-five kilograms so he concluded the plants mass came from the water and not the soil | He was right for the most part |
Joseph Priestly (1771)He put a lit candle in a jar with a piece of a mint plant | The candle soon went out (oxygen had not been discovered yet*) but he knew it "decomposed the air" somehow | There was then no oxygen in the jar | He left the plant in the jar for a while and came back later | He took a magnifying glass and was able to light the candle through the jar, meaning somehow that there was now oxygen in the jar | He concluded then that plants changed the composition of the air |
*Oxygen was discovered in 1772 | | John Woodward (late 1600s)He measured the amount of water he gave to his plant | He gave his plant 76,000 grams of water | However, the plant only grew one gram | So he concluded most of the water that was given to the plant was exhaled through its leaves |
Jan Ingenhousz (1779)He started out similarly to Priestly's experiment; with a lit candle and a plant in a jar | He then put a black cloth over the jar so light could not get into the jar | When he tried to light it later, the candle would not light | He proved that plants need light to change the composition of the air | He also did another experiment where he had an aquatic plant | When there was light, the plant released little bubbles into the water | When there was no light, the plant did not produce bubbles | This further proved that plants need light to change the air |
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